An example of a related art apparatus of this kind will now be described with reference to drawings. FIG. 7 shows a related art reinforcing bar binding machine 1, in which a housing 2 contains therein a binding wire feed unit 3 and a binding wire twisting apparatus 4, a reel base (not shown) being fixed to a rear side surface (rear side of the drawing) of the housing 2, a binding wire reel being mounted on the reel base. A feed roller 5 of the binding wire feed unit 3 is driven by a motor (not shown), and supplies the binding wire wound around a reel therefor to a nose 7, which is formed ahead thereof, through a guide pipe 6. The binding wire twisting apparatus 4 is a unit for tightening the binding wire W wound around reinforcing bar R by the binding wire feed unit 3, by gripping and twisting the binding wire W, and adapted to rotate in the forward and rearward directions a screw shaft 10 connected to reduction gears 9 driven by a motor 8.
As shown in FIG. 8(a), a shaft with a slot 11 is connected rotatably to a front end of the screw shaft 10 by a flanged pin 12 and a slip-off preventing C-ring 13, and the shaft 11 is provided at a front end portion of a slot 11a with a guide pin 14 extending at right angles to the axis thereof. The screw shaft 10 is provided with a sleeve 15, and a sleeve 16 fitted around an outer circumference of the sleeve 15. A ball (not shown) inserted in a hole of the sleeve 15 is engaged with the screw shaft 10, and retained in the hole as the ball is held by the sleeve 16. The sleeve 15 and sleeve 16 are combined with each other, and moved together forward or rearward in accordance with the rotation of the screw. Further, fins 17 are arranged radially on an outer circumferential surface of a rear portion of the sleeve 2.
A pair of hook levers 18 are fixed symmetrically on the opposite sides of the shaft 11 to the front end portion of the slot 16a which is provided at a front portion of the sleeve 16, and a guide recess 18a in an inner portion of the hook levers 18 is engaged with the guide pin 14 of the shaft 11. Hooks 18b at front ends of the two hook levers 18 are expanded and face in the forward direction when the hooks are on standby. When the sleeves 15, 16 are slid forward on the shaft 11, a support shaft of the hook levers 18 is moved forward, and the guide pin 14 is stopped, so that the front ends of the hook levers 18 are closed. Concerning the binding wire twisting apparatus 4, a position in which the sleeves 15, 16 taking the positions shown in the drawing are turned at 90° to cause the hook levers 18 to become horizontal is a standby position, in which a binding wire loop W is gripped from the left and right sides thereof.
The binding wire feed unit 3 and binding wire twisting apparatus 4 are sequence-controlled by a control circuit (not shown), and execute a one-cycle operation including a binding wire feed step and a binding wire twisting step by pulling a trigger lever 19 provided in a grip portion 2a shown in FIG. 7. When the trigger lever 19 is pulled, a binding wire feed motor (not shown) is started, and the binding wire W fed out to the nose 7 by the rotation of the feed roller 5 is bent arcuately along a guide groove in an inner circumference of the nose 7, and wound around a circumference of the reinforcing bar R. When the binding wire finishes being wound a predetermined number of turns around the reinforcing bar, the binding wire feed motor is stopped, and the motor 8 in the binding wire twisting apparatus 4 is then started.
In a standby position shown in FIG. 8(a), a rotation stopping projection 20 provided in the housing is engaged with the fins 17 of the sleeve 16, so that the sleeves 15, 16 and shaft 11 are in a non-rotatable condition. When the screw shaft 10 is rotated counter-clockwise in side elevation taken from the motor side (right side in the drawing), the sleeves 15, 16 are moved forward together, and the hook levers 18 are closed as shown in FIG. 8(b), to grip the binding wire loop. During this time, the fins 17 of the sleeve 16 are disengaged from the rotation-stopping projection 20, and the sleeves 15, 16 and shaft 11 are rotated with the screw shaft 10. As a result, the hook levers 18 twist the binding wire loop, and the reinforcing bars are thereby bound together.
A binding wire cutting unit 21 provided in a path of the binding wire in the nose 7 shown in FIG. 7 is then driven to cut the binding wire in the nose 7, and the motor 8 is rotated reversely at the same time to cause the sleeves 15, 16 to be moved back. The hook levers 18 are then opened to release the binding wire, and the binding wire twisting apparatus 4 returns to a standby condition.